1. Field of the Invention
The present invention relates to a printing apparatus, a printing method, and a program.
2. Description of the Related Art
In general, printing apparatuses which print an image by discharging ink on a printing medium supported by a platen while a printing head having a discharge port array including a plurality of discharge ports which are arrayed is moved in a scanning direction for scanning and conveying the printing medium in a conveyance direction during the scanning have been used.
In such a printing apparatus, when an ink discharge amount per discharge is large, a deviation phenomenon of discharged ink droplets described below is likely to occur. Ink droplets discharged from a printing head drop while involving air existing in a space between the printing head and a printing medium, and accordingly, the space between the printing head and the printing medium becomes in a depressurized state after the discharge of ink. To correct the depressurized state, air in portions in the vicinity of end portions of the discharge port array moves toward the center of the discharge port array, and accordingly, airflows (hereinafter referred to as a “self-airflow” where appropriate) are generated toward the center from the end portions. Due to the self-airflow, a so-called end deviation phenomenon in which ink droplets discharged from discharge ports in end portions of the discharge port array are attracted toward the center of the discharge port array occurs. Note that the larger a discharge amount of ink per discharge is, the larger the self-airflow is, and accordingly, a degree of the end deviation phenomenon of ink droplets is large. Due to the end deviation phenomenon, ink is not attached on regions of the printing medium which is to be printed by discharge ports in the end portions of the discharge port array, and white streaks may appear in a printed image.
Japanese Patent Laid-Open No. 2004-168003 discloses a technique of reducing a conveyance amount of a printing medium relative to a standard amount and reducing a discharge amount of ink from discharge ports in end portions of a discharge port array so that generation of while streaks is suppressed. According to Japanese Patent Laid-Open No. 2004-168003, the printing medium is conveyed such that a discharge port of one end portion of the discharge port array and a discharge port of the other end portion of the discharge port array perform printing on the same region of the printing medium by different scanning operations, and therefore, white streaks generated when a discharge amount of ink is relatively large as described above may be suppressed. Furthermore, when the discharge amount of ink is relatively small, the self-airflow is not generated, and accordingly, black streaks may be generated in a printed image due to the conveyance amount smaller than the standard amount. On the other hand, according to Japanese Patent Laid-Open No. 2004-168003, when a discharge amount of ink is relatively small, the generation of black streaks described above is suppressed by performing correction so that a discharge amount of ink from the discharge ports in the end portions is reduced.
Furthermore, in general, droplet landing accuracy of ink may be deteriorated since a printing medium is lifted relative to a platen which supports the printing medium at a time of printing. Japanese Patent Laid-Open No. 2013-014047 discloses a technique of providing a plurality of suction holes in a platen which supports a printing medium and absorbing the printing medium on the platen by suctioning air through the suction holes.
However, in a printing apparatus having suction means disclosed in Japanese Patent Laid-Open No. 2013-014047, even when the printing method disclosed in Japanese Patent Laid-Open No. 2004-168003 is used, white streaks and black streaks described above may not be efficiently suppressed.
This problem will be described in detail hereinafter.
FIGS. 1A to 1C are diagrams illustrating a state in which strength of an airflow flowing in a space between a printing head 500 and a printing medium 501 obtained when the printing head 500 performs scanning once is changed depending on a position of the printing head 500.
Note that a case where a printing apparatus which prints an image by discharging ink in a vertical downward direction while the printing head 500 having a discharge port array including a plurality of discharge ports arranged in a Y direction (array direction) is moved toward an X direction (scanning direction) is used is illustrated in FIGS. 1A to 1C. Here, a platen 502 which supports the printing medium 501 has a plurality of suction holes 503 formed therein and absorbs the printing medium 501 on the platen 502 by suctioning air through the suction holes 503. Although a platen 2 having only three suction holes 503 is illustrated in FIGS. 1A to 1C for simplicity, a larger number of suction holes 503 are formed in general apparatuses.
FIG. 1A is a diagram illustrating a state in which ink is discharged to a region in the vicinity of an end portion on an upstream side of the printing medium 501 in an X direction immediately after a certain scanning operation is performed once in the X direction of the printing head 500. Since the printing head 500 moves in the X direction for the scanning, airflow 504 is generated from a downstream side to the upstream side in the scanning direction of the printing head 500 in a space between the printing head 500 and the printing medium 501. Furthermore, since air is suctioned through the suction holes 503, an eddy of air is generated toward the suction holes 503 in portions in the vicinity of the suction holes 503. Since the portion in the vicinity of the end portion of the printing medium 501 on the upstream side in the X direction is located near one of the suction holes 503, the portion is affected by the eddy of air, and therefore, an airflow 505 is generated from the downstream side to the upstream side of the scanning direction in the portion between the printing head 500 and the printing medium 501. Specifically, immediately after the certain scanning operation relative to the printing medium 501 is started, an airflow obtained by adding the airflow 504 caused by the scanning and the airflow 505 caused by the suction to each other may be generated in the portion between the printing head 500 and the printing medium 501.
FIG. 1B is a diagram illustrating a state in which the printing head 500 discharges ink to a center region (also referred to as a “region B” hereinafter) in the middle of the certain scanning operation in the X direction. As with the case of FIG. 1A, the airflow 504 is generated from the downstream side to the upstream side in the scanning direction in the space between the printing head 500 and the printing medium 501. On the other hand, since the space between the printing head 500 and the printing medium 501 corresponding to the center region is not in contact with the suction holes 503, the center region is not affected by eddy of air caused by suction through the suction holes 503. Specifically, in the case of FIG. 1B, only the airflow 504 caused by the scanning may be generated in the space between the printing head 500 and the printing medium 501.
FIG. 1C is a diagram illustrating a state when ink is discharged to a region (also referred to as a “region C” hereinafter) in the vicinity of an end portion on the downstream side in an X direction of the printing medium 501 immediately after the certain scanning operation is performed in the X direction. Also in this case, the airflow 504 caused by the scanning is generated in the space between the printing head 500 and the printing medium 501. Unlike the state illustrated in FIG. 1A, one of the suction holes 503 is formed on the downstream side in the X direction relative to the printing head 500 in the state illustrated in FIG. 1C. Therefore, the region is affected by eddy of air through the suction holes 503, and airflow 506 may be generated from the upstream side to the downstream side in the space between the printing head 500 and the printing medium 501. In this way, in the state illustrated in FIG. 1C, the airflow 504 caused by the scanning and the airflow 506 caused by the suction are generated in opposite directions. Specifically, immediately before the certain scanning operation performed on the printing medium 501 is terminated, an airflow obtained by subtraction between the airflow 506 caused by the suction from the airflow 504 caused by the scanning may be generated in the space between the printing head 500 and the printing medium 501.
FIGS. 2A to 2C are diagrams illustrating end deviation phenomena and degrees of the end deviation phenomena corresponding to the positional relationships between the printing head 500 and the printing medium 501 illustrated in FIGS. 1A to 1C, respectively.
Note that, in FIGS. 2A to 2C, states in which the space between the printing head 500 and the printing medium 501 is viewed from the downstream side in the X direction relative to the printing head 500 are illustrated. For simplicity, a case where ink discharge amounts in the states of FIGS. 2A to 2C are substantially the same as one another is described. Furthermore, sizes of circles representing incoming airflows 507 to 509 illustrated in FIGS. 2A to 2C schematically represent strengths of the incoming airflows 507 to 509.
As described above, in the state illustrated in FIG. 2A, the airflow 507 generated in the space between the printing head 500 and the printing medium 501 (hereinafter referred to as an “incoming airflow”) is obtained by adding the airflow 504 caused by the scanning and the airflow 505 caused by the suction to each other, and therefore, the airflow 507 is relatively strong. Accordingly, even when the space between the printing head 500 and the printing medium 501 becomes a depressurized state, the depressurized state is corrected by the airflow 507 or the space becomes a surge pressure state depending on a strength of the incoming airflow 507. Consequently, ink droplets discharged from one of the end portions of the discharge port array is shifted toward an outside of the discharge port array.
On the other hand, in the state illustrated in FIG. 2B, a strength of an incoming airflow 508 is middle. Therefore, correction of the depressurized state by the incoming airflow 508 is not remarkably performed when compared with the state illustrated in FIG. 2A. Accordingly, an amount of shift of ink droplets discharged from the other of the end portions of the discharge port array is smaller than that in the state of FIG. 2A.
Furthermore, in the state of FIG. 2C, the airflow 506 caused by the suction is generated in the direction opposite to the direction of the airflow 504 caused by the scanning, and therefore, an incoming airflow 509 is relatively weak. Therefore, correction of the depressurized state by the incoming airflow 509 is not remarkably performed when compared with the cases of FIGS. 2A and 2B. However, a depressurized state caused by flowing of air in a portion in the vicinity of the other of the end portions of the discharge port array in the array direction toward the center of the discharge port array is remarkably corrected. Consequently, ink droplets discharged from the other of the end portions of the discharge port array land in positions shifted toward the center of the discharge port array. Note that, since the incoming airflow 504 contributes a little to the correction of the depressurized state, a degree of the shift of the ink droplets toward the center of the discharge port array is small when compared with a case where any airflow is not generated.
FIG. 3 is a diagram schematically illustrating an image printed by discharging ink by one scanning operation performed by the printing head 500. For simplicity, a case where printing is performed by one scanning operation on each unit region of the printing medium 501 is described. Furthermore, to suppress generation of white streaks caused by the end deviation phenomenon, the printing medium 501 is conveyed such that a predetermined number of discharge ports Δn may discharge ink in the same regions on the printing medium 501 in different scanning operations. Specifically, positions 511 to 515 in FIG. 3 correspond to first to fifth scanning operations performed on the printing medium 501, and the printing medium 501 is conveyed such that the printing head 500 and the printing medium 501 have these positional relationships in the individual scanning operations.
Here, as described above, in any of the case where printing is performed on the end region on the upstream side (region A) in the X direction of the printing medium 501, the case where printing is performed on the center region (region B), and the case where printing is performed on the end region on the downstream side (region C), influence of an incoming airflow is generated. Therefore, a shift amount toward the end portion of the discharge port array in a Y direction is larger when compared with a case where an incoming airflow is not generated in the region A, the region B, or the region C. Accordingly, even in a case where a discharge amount of ink from discharge ports in the end portions of the discharge port array in the array direction is reduced by a method disclosed in Japanese Patent Laid-Open No. 2004-168003, black streaks are generated in all the regions A to C.
Furthermore, as illustrated in FIGS. 2A to 2C, amounts of shift toward the end portion of the discharge port array in the Y direction becomes large in order from the region A, the region B, to the region C. Accordingly, a density of black streaks 517 generated in the region B is higher than that of black streaks 518 generated in the region C. Furthermore, a density of black streaks 516 generated in the region A is further higher than those of the black streaks 517 and 518 generated in the regions B and C, respectively.
As described above, when printing is performed by a printing apparatus having a suction unit, a magnitude of an incoming airflow varies depending on a position of a printing head in a scanning direction. Therefore, densities of boundary streaks generated in regions on a printing medium corresponding to discharge ports in end portions of a discharge port array in an array direction are different from one another depending on the positions.